均相交叉偶联催化剂的多相化：载体表面效应和孔道限域效应

Cross-coupling reactions have been widely used in the synthesis of pharmaceuticals, fine chemicals and new materials. In order to overcome the difficuties of separation and recycle utilization of the catalysts as well as to reduce the pollution of metal residue existed in the traditional homogeneous palladium catalytic processes, an effective strategy proposed is the heterogenization of homogeneous catalysts. The key factors for heterogeneous catalysis, such as surface effect, spatial confinement and leaching of active species, will be investigated over the palladium catalysts incorporated in the structure of metal-organic frameworks in this project. A series of Pd@MOFs catalysts will be synthesized by incorprating the palladium species on the designed MOFs, which have the same topology, similar porous size and different functional groups on the ligand. The activities of Pd@MOFs catalysts will be evaluated for the oxidation Heck coupling reaction. The relationship between the catalytic properties of Pd@MOFs and the valence, shape as well as the dispersion of palladium species over the catalysts will be explored based on the surface knowledge and theoretical calculation. Moreover, the adsorption/desorption behaviors of substrates and products on the MOFs surface and the intermediates of the reaction will be studied. Combined the microkinetic modeling analysis, the investigation will elucidate the effects of the affinity of substrates and products over the MOFs as well as the spatial confinement of MOFs' cavities on the oxidation Heck reaction. The achievement of this project will provide a suggestion for the strategy of the combination of heterogeneous and homogeneous catalysis.

交叉偶联反应在医药、化工及材料等领域有广泛应用，但传统均相钯催化剂存在催化剂难分离、不能重复使用及残存金属污染产物等缺陷。均相催化剂多相化是解决上述问题的有效途径。本课题针对多相催化中载体表面效应、孔道限域效应及活性组分流失等关键科学问题，开展基于金属有机骨架材料(MOFs)的均相钯催化剂多相化研究。拟设计合成拓扑结构相同、孔道尺寸相近，但表面性质不同的多种MOFs，采用适当条件担载钯活性组分制得系列Pd@MOFs催化剂，以氧化Heck偶联为探针反应评价其催化性能。通过表征Pd在反应过程中的价态、形态及分散度变化，结合表面科学知识及理论计算，揭示MOFs载体表面性质对Pd@MOFs催化性能的影响机制。表征底物/产物在MOFs表面的吸/脱附行为及反应过程中可能存在的中间体，结合微动力学分析，阐明MOFs孔道亲和力和限域作用对氧化Heck反应的影响规律。为多相催化和均相催化的有机结合提供策略。

本项目旨在研究载体表面性质和孔道结构对多相偶联催化剂性能的影响。由含间苯二甲酸单元的多羧酸配体出发，合成了三种以铜基“Paddlewheel”为构筑单元的MOFs材料，CuBTC、pcu-MOF和Cu-TDPAT。研究发现Pd(OAc)2@Cu-TDPAT在Suzuki、Heck及氧化Heck偶联反应中均表现出良好的催化活性，而且催化活性明显高于传统的Pd/C催化剂。重复使用4次活性无明显降低。Pd(OAc)2@Cu-TDPAT催化剂显现出的良好稳定性与Cu-TDPAT骨架中有机配体分子上大量氮原子的存在是分不开的；研究还发现铜基“Paddlewheel”本身对于伯胺、仲胺、氮杂环状胺及酰胺与卤代芳烃间的Ullmann和Goldberg型偶联反应显现出良好的催化活性。目前铜基MOFs在Ullmann和Goldberg型偶联反应的应用尚未见文献报道。另外，利用配位自组装合成了两种新的Porphyrin@MOFs型模拟酶催化剂，CuTNPP@MOF和MnTNPP@MOF，研究发现CuTNPP@MOF对DTBC氧化反应显示良好的催化活性，而MnTNPP@MOF的催化活性仅与pcu-MOF相当。这归因于CuTNPP和pcu-MOF对DTBC氧化反应都有一定的催化活性，而MnTNPP则几乎无活性。而且发现DTBC的氧化产物DTBQ在MOF孔道中吸附会阻碍氧化反应的进行，这是MOF表面性质及孔道结构对DTBC氧化反应产生影响的集中体现。